There are many applications for which delivery of vapor of different types of liquids is desired. In semiconductor processing, for example, it may be desired to deliver photochemicals, such as photoresist chemicals, in vapor form to a process chamber to control the amount and rate at which these photochemicals are applied to a semiconductor wafer. Moreover, the use of many of these photochemicals may result in the production of less than desirable byproducts. To deal with these harmful byproducts and clean a process chamber of these byproducts or other chemicals before another processing stage, water vapor may be delivered to the process chamber. The water vapor may be used to convert these byproducts to less reactive compounds which are more easily disposed of through a chemical reaction.
Both delivering chemicals to a process chamber and the delivery of water vapor to a process chamber in order to react with process byproduct require precise delivery of vapor of different types. To that end, many types of systems have been designed and utilized to deliver vapor at precisely controlled flow rates and pressures for use in a variety of applications.
A typical vapor delivery system, such as one that may be used for delivery of water vapor to a process chamber, employs a vaporizer chamber. At least some portions of this vaporizer chamber are kept at a temperature high enough to vaporize liquid water substantially instantaneously when the liquid water contacts these portions (e.g. 125° C.). The delivery of the vapor formed through this instantaneous vaporization is then controlled with one or more flow controllers.
This type of system has many drawbacks, however. First and foremost, because the vaporization chamber of these types of systems must be maintained at a relatively high temperature these types of systems are relatively inefficient. Part and parcel with this problem, is the problem of condensation. As the water vapor is usually at a relatively high temperature, systems of the type described usually require that components in the flow path of the vapor be maintained at a higher temperature (e.g. 140° C.) than the vapor itself so condensation does not form in the flow path. Not only does this requirement entail higher energy consumption for such systems, but additionally, these higher temperatures may affect the reliability and stability of system components while making the use of such systems hazardous to technicians or other operators.
The use of these high temperatures has other adverse effects as well. By vaporizing the liquid at a higher temperature contaminants within the liquid are more likely to be vaporized, resulting in potential corrosion along the flow path of the vapor, or contamination of the process itself. Additionally, as the flow controllers used to regulate the delivery of vapor may be pressure based mass flow controllers (MFCs), the high temperature used in these systems may cause these pressure based MFCs to drift, affecting the precision with which these systems can regulate the flow of vapor. This drift may be especially prevalent with MFCs that utilize capacitance-based pressure sensors, as in most cases the signal-conditioning electronics are typically positioned very close to the sensors in these types of MFCs.
Other lower temperature systems for delivery vapor have also been tried. These systems suffer from a number of failings as well. The majority of these shortcomings pertain to the inability of these systems to deliver either a high flow rate of vapor or to deliver vapor over long periods of time. In the main, these shortcomings are the result of the conditions required by the majority of these systems to produce vapor, such as that many of these systems may maintain precise equilibrium conditions or that relatively low pressure may need to be applied to create a significant flow of vapor. As a consequence, many of these systems may produce a lower head pressure of vapor, and commensurately be constrained as to the flow rates which they can achieve.
Still other types of systems for the production of water vapor have also been utilized, where the production of water vapor is accomplished by reacting hydrogen and oxygen in the presence of a catalyst. As the reaction utilized to produce vapor in these systems is severely exothermic air-cooling is usually required, making these systems prohibitively expensive for most uses. Additionally, these systems suffer from some of the same problems discussed above. Namely, variation in the reaction used to create water vapor may result in variable flow rates while a single ongoing reaction may not produce the desired flow rate of water vapor.
Thus, as can be seen, systems and methods for the production and delivery of vapor which can maintain consistent, stable and accurate vapor delivery, and which may also operate at sub-atmospheric conditions, are desired.